/**
 * @param {Function} func
 * @param {number} wait
 * @param {boolean} immediate
 * @return {*}
 */
 export function debounce(func, wait, immediate) {
    let timeout, args, context, timestamp, result
    
    const later = function() {
     // 据上一次触发时间间隔
     const last = +new Date() - timestamp
    
     // 上次被包装函数被调用时间间隔 last 小于设定时间间隔 wait
     if (last < wait && last > 0) {
      timeout = setTimeout(later, wait - last)
     } else {
      timeout = null
      // 如果设定为immediate===true，因为开始边界已经调用过了此处无需调用
      if (!immediate) {
       result = func.apply(context, args)
       if (!timeout) context = args = null
      }
     }
    }
    
    return function(...args) {
     context = this
     timestamp = +new Date()
     const callNow = immediate && !timeout
     // 如果延时不存在，重新设定延时
     if (!timeout) timeout = setTimeout(later, wait)
     if (callNow) {
      result = func.apply(context, args)
      context = args = null
     }
    
     return result
    }
   }